Graphics in Games
level of detail in models
lighting
colors
ray casting
terrain maps
texture maps
shadows
take 4390−4391/4451!
How have graphics influenced the
development of games?
What would you do with
substantially more graphics
computing power?
How have graphics influenced the
development of games?
vertical walls/horizontal floors
texture mapping vs modeling detail
fog
games set indoors
What would you do with
substantially more graphics
computing power?
lighting effects−−reflections, shadows
more texture memory
more animation (pipeline latency)
more simulation or AI from CPU
Level of Detail
using simplified versions where
detail is not needed
used throughout the system
polygon meshes
textures (procedural and not)
animation (procedural and not)
where does LOD info come from?
how/when to swap models?
less important if details are truly
minor but pops may attract attention
Level of Detail: Modeling
by hand or automatic?
why artists will do better:
knowledge about the model
facial features, silhouette
why use automatic meshing?
dynamically changing objects
cpu vs. artist time
Art of Low Polygon Modeling
know your limitations
target face count
Quake II 600 faces/character
engine depends on vertices or faces?
know what matters
how will model be seen?
back or front? near or far?
alone or in groups?
properties of model
closed model?
one model or articulated?
organic vs. non−organic
Techniques for Low Poly Models
vertex merge
edge division
edge turn
Automatic Meshing Techniques
off−line (Siggraph Community)
on−line: heuristics for vertex deletion
on−line: parametric surfaces
Progressive Meshing
selecting which edge to collapse next
small details go first
nearly co−planar surfaces need
fewer polygons than areas of high
curvature
.
cost(u,v) = ||u−v|| max (min (1 − fn nn)/2)
n εT
f εTu
uv
where Tu is set of triangles that contain u,
Tuv is set of triangles that contain uv
Progressive Meshing
Lighting
video games are different than stills
or even animations: viewpoint,
object motion
Goals
direct viewer’s attention
emphasize depth and separation
reveal texture, form
create mood
provide exposure and balance
Properties of Lights
quality: hard or soft
intensity: want objects to differ in
brightness for separation and depth
color and pattern: glow from sunset,
grid from bars
direction: frontal, edge/side, back
Direction
top
3H
9H
frontal: key light
strongest, shadows
top
edge/side:
contours,
texture
side
12H
12V
3V
9V
6H
6V
12H
3H
9H
6H
top
back: separate
from background
side
12H
3H
9H
6H
12V
3V
9V
6V
Key light
casts shadows
chief light source
diagonally from front, high
Fill light
soften shadows
lower intensity
positioned lower
Back light
separate figure from background (3d)
mid−level intensity
above figure
Key
Key
F
F
R
Key
F
F
Color Theory
use color palette to set mood
color temperature
warm: red, red−orange, yellow,
yellow−green
cold: violet, blue, green, green−yellow,
blue−green
weight: darker−>heavier
depth: grey−> more distant
visibility:
black/yellow
green/white
red/white
blue/white
white/blue
black/white
Color Schemes that Work
monochromatic
just primary colors
all warm or all cool
contrast of warm and cool
color and its complement
Raycasting
Wolfenstein 3D in 1992
subclass of ray tracing
Raytracing
hidden surface removal
transparency
reflections
refractions
ambient lighting
shadows
Raycasting
grid world plane
number of rays −> horizontal resolution
+ subsampling?
tables of slopes for efficiency
World
O
walls at 90 wrt to floor
walls made of uniform cubes
floor flat
each cube consists of
64x64 smaller units
Viewer
player’s height, field of view
x,y position of player
facing direction (yaw)
Finding Walls
FOV = 60
screen size = 320
ray = viewing angle −30
for (col = 0; col++, ray += 60/320, col<320)
follow ray until hit wall
record distance to wall
Finding Intersections
find intersection
points with the grid
fixed number of
ray angles: 360/(60/320)
use a table for the slope
Horizontal Intersections
find first intersection
check grid (wall or !wall)
if wall compute distance
if !wall
find next intersection
x’ = x+xa, y’ = y+ya
xa = table lookup
ya = grid height
α
xa?
ya = 64
xa = 64/tanα
Vertical intersections are
similar−−look up ya, xa is grid width
Finding Distance
d = sqrt((px −dx)2 + (py−dy)2)
d = abs(px −dx) / cos(α)
d = abs(py −dy) / sin(α)
dx,dy
α
px,py
table look−up for cos, sin
finite number of values for α
Improvements
doors and windows
45o walls
platforms and ramps
Drawing Walls
find height of projected wall slice
wall
w
projection
plane
pw
dist pp
dist pw
pw/dist pp = w/dist pw